Fix #240, default implementation of observers.

Requries user who overrides one observer to override them all.
Consider using a dictionary for user to override only some observers.

src/venturescript/vscgpm.py

@@ -14,6 +14,7 @@
 #   See the License for the specific language governing permissions and
 #   limitations under the License.
 
+import itertools
 import base64
 import copy
 import math
@@ -23,6 +24,8 @@
 
 import venture.shortcuts as vs
 
+from venture.exception import VentureException
+
 from cgpm.cgpm import CGpm
 from cgpm.utils import config as cu
 from cgpm.utils import general as gu
@@ -71,7 +74,9 @@ def __init__(self, outputs, inputs, rng=None, sp=None, **kwargs):
             raise ValueError('source.inputs list disagrees with inputs.')
         self.inputs = inputs
         # Check overriden observers.
-        if len(self.outputs) != self.ripl.evaluate('(size observers)'):
+        num_observers = self._get_num_observers()
+        self.obs_override = num_observers is not None
+        if self.obs_override and len(self.outputs) != num_observers:
             raise ValueError('source.observers list disagrees with outputs.')
         # XXX Eliminate this nested defaultdict
         # Inputs and labels for incorporate/unincorporate.
@@ -174,12 +179,20 @@ def _predict_cell(self, rowid, target, inputs, label):
             '((lookup outputs %i) %s)' % (i, sp_args), label=label)
 
     def _observe_cell(self, rowid, query, value, inputs):
+        output_id = self.outputs.index(query)
         inputs_list = [inputs[i] for i in self.inputs]
-        label = '\''+self._gen_label()
-        sp_args = str.join(' ', map(str, [rowid] + inputs_list + [value, label]))
-        i = self.outputs.index(query)
-        self.ripl.evaluate('((lookup observers %i) %s)' % (i, sp_args))
-        self.obs[rowid]['labels'][query] = label[1:]
+        label = self._gen_label()
+        if self.obs_override:
+            qlabel = '(quote %s)' % (label,)
+            sp_args = ' '.join(map(str,
+                itertools.chain([rowid], inputs_list, [value, qlabel])))
+            self.ripl.evaluate('((lookup observers %i) %s)'
+                % (output_id, sp_args))
+        else:
+            sp_args = ' '.join(map(str, itertools.chain([rowid], inputs_list)))
+            self.ripl.observe('((lookup outputs %i) %s)'
+                % (output_id, sp_args), value, label=label)
+        self.obs[rowid]['labels'][query] = label
 
     def _forget_cell(self, rowid, query):
         if query not in self.obs[rowid]['labels']:
@@ -255,6 +268,14 @@ def _check_matched_inputs(self, rowid, inputs):
             raise ValueError('Given inputs contradicts dataset: %d, %s, %s' %
                 (rowid, inputs, self.obs[rowid]['inputs']))
 
+    def _get_num_observers(self):
+        # Return the length of the "observers" list defined by the client, or
+        # None if the client did not override the observers.
+        try:
+            return self.ripl.evaluate('(size observers)')
+        except VentureException:
+            return None
+
     @staticmethod
     def _obs_to_json(obs):
         def convert_key_int_to_str(d):

tests/test_vscgpm.py

@@ -60,16 +60,13 @@
   (lambda (rowid w value label)
     (observe (simulate_y ,rowid ,w) value ,label))]
 
-[define observers (list observe_m
-                        observe_y)]
-
 [define inputs (list 'w)]
 
 [define transition
   (lambda (N)
     (mh default one N))]
-"""
 
+"""
 
 source_concrete = """
 define make_cgpm = () -> {
@@ -100,19 +97,42 @@
     $label: observe simulate_y($rowid, $w) = value;
 };
 
-define observers = [observe_m, observe_y];
-
 define inputs = ["w"];
 
 define transition = (N) -> {
     mh(default, one, N)
 };
+
 """
 
+# Define source with client overriding observers.
+source_abstract_observers_good = source_abstract + \
+    '[define observers (list observe_m observe_y)]\n'
+source_abstract_observers_bad = source_abstract + \
+    '[define observers (list observe_m observe_y 2)]\n'
+
+source_concrete_observers_good = source_concrete + \
+    'define observers = [observe_m, observe_y];\n'
+source_concrete_observers_bad = source_concrete + \
+    'define observers = [observe_m, observe_y, 2];\n'
+
+# Define test cases.
 Case = namedtuple('Case', ['source', 'mode'])
 cases = [
-    Case(source_abstract, 'church_prime'),
-    Case(source_concrete, 'venture_script'),
+    Case(source_abstract,                   'church_prime'),
+    Case(source_concrete,                   'venture_script'),
+    Case(source_abstract_observers_good,    'church_prime'),
+    Case(source_concrete_observers_good,    'venture_script'),
+]
+
+CaseObs = namedtuple('Case', ['source', 'obsok', 'mode'])
+casesObs = [
+    CaseObs(source_abstract,                   True, 'church_prime'),
+    CaseObs(source_concrete,                   True, 'venture_script'),
+    CaseObs(source_abstract_observers_good,    True, 'church_prime'),
+    CaseObs(source_concrete_observers_good,    True, 'venture_script'),
+    CaseObs(source_abstract_observers_bad,     False, 'church_prime'),
+    CaseObs(source_concrete_observers_bad,     False, 'venture_script'),
 ]
 
 @pytest.mark.parametrize('case', cases)
@@ -133,6 +153,14 @@ def test_wrong_inputs(case):
     with pytest.raises(ValueError):
         VsCGpm(outputs=[1,2], inputs=[3,4], source=case.source, mode=case.mode)
 
+@pytest.mark.parametrize('case', casesObs)
+def test_wrong_observers(case):
+    try:
+        VsCGpm(outputs=[0,1], inputs=[2], source=case.source, mode=case.mode)
+        assert case.obsok
+    except ValueError:
+        assert not case.obsok
+
 @pytest.mark.parametrize('case', cases)
 def test_incorporate_unincorporate(case):
     cgpm = VsCGpm(outputs=[0,1], inputs=[3], source=case.source, mode=case.mode)